Since the introduction of emergency number dialing in the 1960's, almost every telephone service provider in almost every country has some form of emergency number. A person can dial the emergency number from virtually any telephone (even a pay phone) and be connected to emergency services. Emergency numbers are selected so that they can be easily recalled and dialed. In the U.S., for example, the number is "911." In Sweden, the number is "112."
Emergency number dialing is also practiced in wireless networks. Most wireless stations recognize one or more emergency numbers (911, 999, *999, etc.) and access the wireless network differently than in a regular call. A special emergency message is sent to the wireless system, which causes the wireless system to bypass most or all of the call setup (digit analysis and so forth) and authentication steps commonly performed. A call is immediately set up directly to the public safety answering point. Even a wireless station that is not yet activated can place an emergency call.
Emergency number dialing, however, is not quite as simple or straight forward in a new and rapidly growing sector of the local telephone market. Fixed cellular is becoming the solution of choice for providing telecommunication services for a number of diverse applications. In fixed cellular, one or more standard telephones (sometimes called plain old telephones or "POTS"), facsimile machines, modems, etc. in a home or office are connected via normal premises wiring to a line interface controller and then to a cellular terminal. The cellular terminal provides service for the fixed cellular telephones through the air interface of a cellular communications system, just like any other cellular communication device.
Telecommunications providers attempting to enter the local service market use fixed cellular to serve a number of customer premises with a minimal investment in infrastructure. The cost of running wire through the entire area to serve a few customers is avoided. More importantly, erecting a few cellular towers and installing a little customer premise equipment may rapidly develop areas that did not formerly have telephone service at all.
As stated above, the telephones in fixed cellular systems are essentially identical to those used in wireline service. In fixed cellular systems, however, the steps for placing a call are slightly different. Generally, there are three approaches in common usage for placing a call in the fixed cellular environment: send key dialing, timeout dialing and digit-by-digit dialing.
Send key dialing is similar to the standard operation of a mobile telephone. At the conclusion of entering the destination telephone number, the user presses a predefined key on the telephone to instruct the fixed wireless system to send the call to the wireless network. The send key is usually the "#" or ".star-solid." key on a standard telephone keypad. Once the call is finally sent to the wireless network, it receives the same priority and processing as any other emergency access. However, if the user forgets to dial the send key (not a common operation to people conditioned to normal landline dialing, especially in an emergency), the emergency call will never be sent.
In timeout dialing, the fixed cellular service attempts to analyze the dialed digits to determine the last number dialed by the subscriber so that the user does not have to press a send key. If a timer expires without any keys being pressed (typically 3-5 seconds from the last number dialed) the digits are sent to the wireless network to set up a call. In emergencies, the user must wait for the Umeout, usually without any audible feedback from the telephone. In an emergency, a user may become confused after dialing the emergency number and perhaps think that the call did not go through. If the user hangs up and tries again, the delay of call completion increases.
Digit-by-digit dialing automatically places a cellular call to a predefined telephone number at the mobile switching system (sometimes called a "roamer port") as soon as the user starts dialing. The dialed digits are collected and transmitted to the mobile switching system for analysis and call connection. The cellular system does not recognize the access as an emergency, since the first part of the cellular access is to the roamer port. Further, the mobile station to cellular network interaction is no different from any other call. If the serial number checking or authentication fail during the access, then the call is not completed at all.